I second charcoal. It is very versatile. I have one with a modest, subdued pinstriping and it is my go-to suit. Make sure it is tailored (altered, not built from scratch) to fit your body and not "off the shelf". It makes a huge difference. Also second what is said above about only having one. You just aren't going to need it after you get hired. Nobody is going to care at a multi day interview as long as you change your shirt and tie. You will probably have your jacket off for half the day anyway.